Method of manufacturing permanent magnets



METHOD OF MANUFACTURING PERMANENT MAGNETS Robert Loosjes, Cornelis Frederik Veenemans, and Gerard Hugo Weber, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N .Y., a corporation of Delaware No Drawing. Filed Dec. 21, 1955, Ser. No. 554,605

Claims priority, application Netherlands Dec. 21, 1954 8 Claims. (Cl. 25262.5)

Permanent magnets which substantially consist of simple crystals or mixed crystals having a constitution according to the formula M Ca O.6Fe O where M is one or more of the metals Ba, Sr or Pb and O.6x- -l, are known (see for example French patent specification No. 1,048,792 or U.S. Patent 2,672,777, and Philips Technical Review, volume 13, No. 7, January 1952, pages 194-208). It is also known (see French patent specification 1,080,514, or U.S. Patent 2,762,778) to manufacture crystal oriented or anisotropic permanent magnets which consist of such materials. As pointed out in those patents and publications, the constituent essential to the magnetic properties of the material is MFe O or MO.6Fe O M being barium, strontium or lead, or mixed crystals of two or more of those compounds. Calcium may be substituted for one of said metals in an amount up to 0.4 as an atomic fraction of those metals. Thus, the formula of the essential constitutent may be written (to include calcium) as M Ca 0.6Fe O or x being greater than 0.6 and less than 1. Other, and nonessential constituents may and often are present. Thus, commonly, an excess of one of the oxides, preferably the bivalent metal oxide, is employed in the starting mixture and this excess may remain as unreacted or partially reacted material in the final composition, for as noted in U.S. Patent 2,762,777, these materials may be prepared by mixing the oxides in a relatively wide range of proportions representing a significant departure from the ratio appearing in the constitutent essential to the magnetic properties of the material.

As described in U.S. Patent 2,762,778, this material can be made anisotropic by orienting the crystals while they are in a mobile state. Preferably this is accomplished by suspending the material, in finely-divided form, in a liquid arranged between the poles of magnet. The material is preferably compressed during orientation and then sintered at a temperature of about 1100 to 1450 C. to form a coherent body. This method has already led to the manufacture of permanent magnets having a (BH) -value exceeding 2 10 gauss-oersted. The mechanical properties also of the magnets thus produced are generally satisfactory. However, the method concerned does not give complete satisfaction when magnets of more or less complicated shape have to be manufactured. It should be borne in mind that the dies which must be used for carrying out said method must obviously also frequently break down owing to wear when comparatively large quantities of water are drawn off.

Obviously, said difficulties can be obviated by manufacturing permanent magnets of simple shape and subsequently shaping them mechanically into the required complicated form, however, this method does not completely satisfy either, since the members concerned are not very suitable to mechanical working, for they are too hard.

As an alternative, it has been proposed in the French patent specification No. 1,080,514 mentioned hereinbefore to compress the particles of the crystal powder required to be worked up into a permanent magnet as such, that is to say without the use of any liquid, the particles of the powder still retaining a certain amount of freedom of movement relative to each other, in a magnetic field (hereinafter referred to as dry moulding method) and subsequently to sinter the produced moulding to form a permanent magnet. The mechanical properties and the compactness of the permanent magnets produced so far by this method, however, are unsatisfactory.

The invention solves the problem of manufacturing anisotropic permanent magnets of the kind described and having a comparatively complicated structure, by the use of a method which comprises features both of the wet and of the dry moulding method. According to the invention, one'proceeds as follows. Similarly to the wet moulding method, the permanent magnet powder is suspended in an indifferent liquid, for example water, and the liquid is removed from the suspension, for example by filtering, while the suspension is arranged between the poles of a magnet. Thus, a conglomerate is obtained which has a magnetic directive effect: it is magnetically anisotropic. The conglomerate is granulated, for example by means of a sieve, through which the solid substance is pressed. The granulate produced is subsequently arranged in a moulding die in which it is compressed between the poles of a magnet. The molded product obtained, the (magnetically anisotropic) grains of which due to the last operation are comparatively satisfactorily parallel oriented magnetically, finally is sintered again to form the ultimately required permanent magnet. This method permits the production of permanent magnets having a (BH) -value exceeding approximately 1.5 X 10 gauss-oersted. Preferably the granulate, prior to being worked up into a molded product in the above-mentioned manner, has a substance added to it which imparts a satisfactory coherence to it and nevertheless does not increase the friction between the grains during the molding process. Suitable substances are particularly solid organic substances which are liquefied under a slight pressure (of less than 500 kg./cm. Camphor or chemically related substances have proved very suitable for the purpose concerned; thus, camphor is liquefied at a pressure of from to kg./cm. Preferably the camphor or similar substance are added in the form of an alcoholic solution, for example a solution of 2% by weight, which is sprayed over the granulate required to be molded. Instead of camphor or a similar substance use may, for example, be made of paraflin.

In order that the invention may readily be carried out, two examples will now be described in detail.

Example I Finely powdered barium carbonate, BaCO and ferric oxide, Fe O are thoroughly mixed at a ratio of 1.1:6 mol. The mixture is compressed to form blocks and these blocks are fired for approximately 15 minutes at 1280 C. After cooling, the blocks are pulverised and the obtained powder is worked up into a suspension after the addition of a small amount of water and 1% by weight of calcium carbonate, CaCO From this suspension the water is removed by filtering in a magnetic field, after which the filter cake is dried by exposure to air. The airdried substance is subsequently pressed through a sieve having meshes of approximately 2 x 2 mms. The grains produced are compressed in a magnetic field and finally fired for approximately 5 minutes at approximately 1250" C.

The properties of the permanent magnet produced by this method were as follows:

Br=3050 gauss H 1450 oersted H =1600 oersted (BI-U 1.8 X 10 gauss-oersted (at H: 1000 oersted) Example 11 pressed through a sieve having meshes of approximately 1 x 1 mm. An alcoholic solution of 2% by weight of camphor is sprayed over the grains produced. The alcohol is evaporated by exposing the granulate to air for some time. The grains mixed with camphor are subsequently compressed in a magnetic field and the molded product thus obtained is finally fired for approximately minutes at approximately 1240 C.

The properties of a permanent magnet produced in this manner were as follows:

Br=3340 gauss H =1240 oersted H =1280 oersted (BI-I),,,,,, =2.3 l0 gauss-oersted (at H=1100 oersted) What is claimed is:

1. In the manufacture of a permanent anisotropic magnet, the steps of suspending in a chemically inert liquid crystals of a material having a composition M Ca 0. 61 9 0 in which M is at least one of the metals selected from the group consisting of barium, strontium and lead, and x is at least equal to 0.6 and not greater than 1, filtering the liquid under the action of a magnetic field to thereby produce a magnetically anisotropic conglomerate, granulating the conglomerate, molding the conglomerate under the action of a magnetic field to produce a magnetically anisotropic body, and sintering said body at a temperature of about 1100 to 1400 C. to produce a highly-coherent permanent magnet body having a (BH) 1.5)( gaussoersted.

2. In the manufacture of a permanent anisotropic magnet, the steps of suspending in a chemically inert liquid crystals of a material having a composition in which M is at least one of the metals selected from the group consisting of barium, strontium and lead, and x is at least equal to 0.6 and not greater than 1, filtering the liquid under the action of a magnetic field to thereby produce a magnetically anisotropic conglomerate, granulating the conglomerate, adding to the granulated conglomerate an organic binder adapted to increase cohesion between grains without increasing friction therebetween during molding, molding the conglomerate under the action of a magnetic field to produce a magnetically anisotropic body, and sintering said body at a temperature of about 1100 to 1400 C. to produce a highly-coherent permanent magnet body having a (BI-l) value exceeding approximately 1.5 x10 gauss-oersted.

3. In the manufacture of a permanent anisotropic magnet, the steps of suspending in a chemically inert liquid crystals of a material having a composition in which M is at least one of the metals selected from the group consisting of barium, strontium and lead, and x is at least equal to 0.6 and not greater than 1, filtering the liquid under the action of a magnetic field to thereby produce a magnetically anisotropic conglomerate, granulating the conglomerate, adding to the granulated conglomerate an organic binder adapted to be liquefied at a pressure of less than about 500 lag/cm. and further adapted to increase cohesion between grains without increasing friction therebetween during molding, molding the conglomerate under the action of a magnetic field to produce a magnetically anisotropic body, and sintering said body at a temperature of about to 1400 C. to produce a highly-coherent permanent magnet body having a (BI-I) value exceeding approximately 1.5 10 gaussoersted.

4. In the manufacture of a permanent anisotropic magnet, the steps of suspending in a chemically inert liquid crystals of a material having a composition in which M is at least one of the metals selected from the group consisting of barium, strontium and lead, and x is at least equal to 0.6 and not greater than 1, filtering the liquid under the action of a magnetic field to thereby produce a magnetically anisotropic conglomerate, granulating the conglomerate, adding camphor to the granulated conglomerate, molding the conglomerate under the action of a magnetic field to produce a magnetically anisotropic body, and sintering said body at a temperature of about ll00 to 1400 C. to produce a highly-coherent permanent magnet body having a (BI-U value exceeding ap proximately 1.5 10 gauss-oersted.

5. In the manufacture of a permanent anisotropic magnet, the steps of suspending in a chemically inert liquid crystals of a material having a composition in which M is at least one of the metals selected from the group consisting of barium, strontium and lead, and x is at least equal to 0.6 and not greater than 1, filtering the liquid under the action of a magnetic field to thereby produce a magnetically anisotropic conglomerate, granulating the conglomerate, adding an alcoholic solution of camphor to the granulated conglomerate, molding the conglomerate under the action of a magnetic field to produce a mag netically anisotropic body, and sintering said body at a temperature of about 1100 to 1400 C. to produce a highly-coherent permanent magnet body having a (EH) value exceeding approximately 1.5 10 gaussoersted.

6. In the manufacture of a permanent anisotropic magnet, the steps of suspending in a chemically inert liquid crystals of a material having a composition in which M is at least one of the metals selected from the group consisting of barium, strontium and lead, and x is at least equal to 0.6 and not greater than 1, filtering the liquid under the action of a magnetic field to thereby produce a magnetically anisotropic conglomerate, granulating the conglomerate, spraying the granulated conglomerate with an alcoholic camphor solution, molding the conglomerate under the action of magnetic field to produce a magnetically anisotropic body, and sintering said body at a temperature of about 1100 to 1400 C. to produce a highly-coherent permanent magnet body having a (BH) value exceeding approximately 1.5 10 gauss oersted.

7. In the manufacture of a permanent anisotropic mag- M Ca 0.61 6 0 in which M is at least one of the metals selected firom the group consisting of barium, strontium and lead, and x is at least equal to 0.6 and not greater than 1, filtering the liquid under the action of a magnetic field to thereby produce a magnetically anisotropic conglomerate, granulating the conglomerate, adding paraflin to the granulated conglomerate, molding the conglomerate under the action of a magnetic field to produce a magnetically anisotropic body, and sintering said body at a temperature of about 1100 to 1400 C. to produce a highly-coherent permanent magnet body having a (BH),,,,, value exceeding approximately 1.5 X gauss-oersted.

8. In the manufacture of a permanent anisotropic magnet, the steps of suspending in a chemically inert liquid crystals of a material having a composition in which x is at least equal to 0.6 and not greater than 1, filtering the liquid under the action of -a magnetic field to thereby produce a magnetically anisotropic conglomerate, granulating the conglomerate, spraying the granulated conglomerate with an alcoholic camphor solution, molding the conglomerate under the action of a magnetic field to produce a magnetically anisotropic body, and sintering said body at a temperature of about 1100 to 1400 C. to produce a highly-coherent permanent magnet body having a (BH) value exceeding approximately 1.5 x10 gaussoersted.

References Cited in the file of this patent UNITED STATES PATENTS 2,535,025 Albers-Schoenberg Dec. 26, 1950 2,565,861 Leverenz Aug. 28, 1951 2,705,701 Crowley Apr. 5, 1955 2,714,580 Dean et al Aug. 2, 1955 2,723,238 Simpkiss Nov. 8, 1955 2,762,777 Went et a1 Sept. 11, 1956 2,849,312 Peterman Aug. 26, 1958 2,854,412 Brockman Sept. 30, 1958 FOREIGN PATENTS 516,598 Belgium June 29, 1953 521,244 Belgium Jan. 6, 1954 1,080,514 France June 2, 1954 OTHER REFERENCES Elec. Eng, July 1952, pages 644-647. Reviews of Modern Physics, vol. 25, No. 1, January 1953.

Phillips Tech. Review, vol. 16, November 1954, pages 141-146.

UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2,960,470 November 15 1960 Robert Loosjes et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below. I

Column 1, line .21 for "U, 8'. Patent 2 672,777" read U. S. Patent 2,762,777

sighed and sealed this 9th day of May 1961.

(SEAL) Arrest:

ERNEST W, SWIDER DAVID LADD Attesting Officer Commissioner of Patents 

1. IN THE MANUFACTURE OF A PERMANENT ANISOTROPIC MAGNET, THE STEPS OF SUSPENDING IN A CHEMICALLY INERT LIQUID CRYSTALS OF A MATERIAL HAVING A COMPOSITION 